An RFID tag is well known. The RFID tag is attached on clothes, for example. The RFID tag includes an inlet airtightly enclosed within a sealing piece. The sealing piece is made of rubber, for example. The inlet includes a semiconductor chip. The RFID tag is configured to transmit and receive a predetermined radio signal in accordance with the operation of the semiconductor chip. A pair of reinforcing pieces is embedded within the sealing piece. The semiconductor chip is interposed between the reinforcing pieces. The reinforcing pieces are made of plastic, for example.    Publication 1: JP Patent Application Laid-open No. 61-204788    Publication 2: JP Patent Application Laid-open No. 2002-366918    Publication 3: JP Patent Application Laid-open No. 2008-021033    Publication 4: JP Patent Application Laid-open No. 2005-242723    Publication 5: JP Patent Application Laid-open No. 2008-046668    Publication 6: JP Patent Application Laid-open No. 2007-072829    Publication 7: JP Patent Application Laid-open No. 11-296642    Publication 8: JP Patent Application Laid-open No. 2006-031089
When the clothes are washed or spin-dried, an RFID tag suffers from stress as a result of twisting, bending, shrinkage or elongation of the clothes. Bending stress is generated in the sealing piece, for example. The reinforcing pieces are configured to absorb the stress. However, since the reinforcing pieces separately absorb the stress, the reinforcing pieces are not allowed to have a sufficient rigidity. Consequently, if the sealing piece suffers from a relatively large stress, the semiconductor chip can be damaged.